Dissertation
Stöorungstheoretische Behandlung der Strahlungstransportgleichung in dreidimensionalen, bewegten Medien und Anwendung auf Akkretionsscheiben

(Perturbation approach for the radiative transfer equation for 3D moving media and application to accretion disks)


Nikolai Kryzhevoi

Abstract:
The multidimensional radiative transfer equation is solved by means of a perturbation approach in which the full solution is represented by a sequence of 1D solutions. Since the solutions of the higher perturbation orders are given explicitly, and the methods used for the solution of the zero order equation are largely analytical, the corresponding code is more efficient than general multidimensional radiative transfer codes. To examine this iterative procedure the radiation field of a geometrically thin slowly rotating accretion disk is calculated. The method is the improvement of those methods which treat the accretion disk as a system of independent rings because the interaction of the rings is taken into account in the higher perturbation orders. The influences of radial gradients, velocity field etc. on the line profile are discussed. Furthermore, under assumption of the two-stream approximation the analytical solution of the plane-parallel radiative transfer equation is found for a large variety of the internal distribution of the de-excitation coefficient epsilon. A new method for the solution of the equation with the stochastic epsilon is proposed. In addition, an improved separable approximation method enable us to obtain fast and accurate solution of the basic plane-parallel radiative transfer equation without angle and space discretization.


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